1. Field of the Invention
This invention relates to a truss shoe and, more particularly, to a truss shoe for a mine roof support truss system to produce a desired tension for supporting a wide variety of mine roof conditions.
2. Description of Related Art
Truss-type mine roof supports are well known in the art of supporting the roof of an underground passageway, such as a mine passage. A basic truss system includes one or more rods extending horizontally the width of the mine passage adjacent the roof and connected at their ends to anchor bolts which extend at an angle adjacent the ribs of the passageway into the rock strata over a solid pillar. The rods are tensioned and vertical components of compressive forces are transmitted into the solid material over the pillars, as opposed to the unsupported rock material immediately above the passageway.
With this arrangement, a truss system shifts the weight of the rock strata from over the mined-out passageway back onto the pillars. The desirability of truss systems has been enhanced by the development of roof bolting machines that can convert from vertical to angle drilling. Conventionally, holes are drilled into the mine roof at a 45° angle from horizontal adjacent to the mine rib so that the holes extend into the supported rock structure over a pillar. To ensure adequate anchorage over the pillar at the rib line, the bolts extend up to six or seven feet into the supported structure over the pillar.
Once the angle holes are drilled into the strata over the pillars at the rib line, anchor bolts are inserted into the drilled holes and are secured in place using mechanical expansion shell assemblies and/or with a resin made from a mixture of a resin component and an epoxy component. This arrangement ensures adequate anchorage over the rib line for bolts that extend in length up to six feet (1.8 meters) or greater. Before the bolts are inserted in the drilled holes, truss shoes or bearing blocks are positioned on the bolt at the emergent end of the bolt from the hole. As the bolts are securely anchored in the bore holes, the bearing surfaces of the truss shoes or bearing blocks are compressed into engagement with the mine roof.
For an uneven mine roof or a roof having severely potted areas, the truss shoe or bearing block preferably has sufficient bearing surface to contact the mine roof so that the truss shoe is correctly positioned for engagement with the horizontal truss members. Once the truss shoes or bearing blocks are securely positioned at the mine roof adjacent the ribs, the horizontal truss members are assembled and connected to the truss shoes. The truss members are tightened to a preselected torque to exert tension on the truss members so that the weight of the rock strata over the mined out area beneath the roof is shifted along the horizontal truss members upwardly into the solid rock strata over the pillars at the ribline.
A wide variety of truss hardware is commercially available to form a truss system between the anchored angle bolts. The truss hardware is connected under tension to the truss shoes that are held tightly against the mine roof by the anchored angle bolts.
U.S. Pat. No. 5,302,056 discloses such a truss system. In that system, there is provided a roof support for an underground passageway that includes first and second truss brackets. The first and second truss brackets are secured to the roof of the underground passageway adjacent to opposing ribs of the underground passageway. The truss brackets each include a roof engaging surface positioned in contact with the roof and a truss supporting arm member extending from the roof engaging surface. The truss supporting arm member is positioned horizontally relative to the roof engaging surface. A truss arrangement extends between the first and second truss brackets for applying an uplifting force to the roof to support the roof above the passage. The truss arrangement includes a pair of U-shaped members releasably engaged to the first and second truss brackets. Each of the U-shaped members is supported in a vertically hanging position by the supporting arm members. The arm members each include an end portion arranged to retain the U-shaped member for horizontal movement on the truss bracket. Tension is applied to the truss members, with the U-shaped members engaged to the truss brackets to apply an uplifting force to the roof.
DYWIDAG-Systems International (DSI) manufactures and sells a bar cable truss system including a pair of truss shoes, a pair of inclined bolts, and a truss assembly. Each truss shoe attaches to a roof through an inclined bolt. Each truss shoe includes a surface for contacting the roof and a truss supporting member. The truss assembly extends between the truss supporting members of the pair of truss shoes for applying an uplifting force to the roof to support the roof above the passage. The truss assembly includes a pair of cables engaged to the truss shoes through a slot and opening configuration in the truss supporting member.
Although the truss shoes presently available for use with mine roof support systems are acceptable for their intended purposes, it is appreciated by those skilled in the art that providing additional truss shoe designs provide a wider selection of truss shoes for use with the mine roof support system to provide support for different types of mine roof surface conditions.